Bowyers Bible 4 question ???

[wakosama]

"Trapping" the back of a bow is mentioned several times.  No definition or explanation I can find.  Can anyone explain it in detail please?  Thanks.

[JackCrafty]

Trapping is short for a trapezoid cross section where the back is less wide than the belly.  This cross section is used for wood that is strong in tension and very weak in compression.

[adb]

Trapping is created by cutting small facets off the corners of the backing material. By small facets, I mean usually an eighth of an inch or so. Works great for hickory or bamboo, both of which excel at tension. Most bows do much better if you round off and eliminate all square edges. Square edges concentrate pressure, and are weak spots,which are more prone to lifting a splinter.

[Pat B]

I have used trapping on boo backed bows when I realized the bow was taking too much set. This reduced the tension strength and lessened the set of the final bow. You can also use it with self bows if you want to use a less appropriate design for a particular wood.        Pat

[benjamin]

Wouldn't trapping do the same thing as using a crowned stave? Here we've scientifified strength to whatever ratios and come up with the same OLD design Adam probably used. Just goes to show you can superanalyze something or just go with tradition and get to the same conclusion. "Primitive" doesn't mean "stupid".

[wakosama]

Thanks... I understand.  Now... say I'm using boo back.  Been advised to taper backing to sharp edge at the side of the limb so thickness is less at tips, alot of work...  Instead: 'trapping' = I keep the boo a constant thickness  following the limb profile then bevel it narrower on the back.  Sounds easier with hand tools, after the bow is glued up, and can be part of limb tillering... maybe.

So... do I 'trap' just the whole thickness of the backing, or the whole thickness of the limb, so the belly wood is also 'trapped'.  Sounds like only the backing...

I can get detailed if advised.

Thanks
 

[Pat B]

You need to pre shape the boo then thin it to get it thin enough its full length. You can still trap the bow by making the belly wider than the backing. Trying to cut corners because it is a lot of work will end up in broke bows and frustrated bowyer.       Pat